To start with, think of class as an "Idea", it is something that is different from others and has a unique behavior, it can be a person, an aircraft or anything else. The objects are just the example of that given idea, like you and me or a Sukhoi-30. In other words, a class is a blueprint from which objects are constructed. The objects represents the particular instance of that class, like people belonging to the same city, and the aircraft's produced of a given type.